University of Birmingham Potential for intracranial movements in pterosaurs Prondvai, Edina; si, Attila Document Version Publisher's PDF, also known as Version of record Citation for published version (Harvard): Prondvai, E & si, A 2011, 'Potential for intracranial movements in pterosaurs', The Anatomical record. Link to publication on Research at Birmingham portal General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. 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Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive. If you believe that this is the case for this document, please contact [email protected] providing details and we will remove access to the work immediately and investigate. Download date: 02. Oct. 2021 THE ANATOMICAL RECORD 294:813–830 (2011) Potential for Intracranial Movements in Pterosaurs 1 † 2 EDINA PRONDVAI * AND ATTILA OSI 1Department of Paleontology, Eo¨tvo¨s Lora´nd University, Budapest, H-1117, Hungary 2Hungarian Academy of Sciences—Hungarian Natural History Museum, Research Group for Paleontology, Budapest, H-1083, Hungary ABSTRACT Based on comparative anatomical, morphological, and phylogenetic considerations the potential of pterosaurs for cranial kinesis is assessed. Our investigation shows that whereas skeletally mature derived pterodac- tyloids have completely fused, rigid and doubtlessly akinetic skulls, skele- tally immature derived pterodactyloids and more basal pterosaurs possess key features in the morphology of their otic and basal joints that are suggestive of cranial kinesis, namely streptostyly. In addition, ptero- saurs exhibit an evolutionarily informative trend in the degree of cranial ossification, where it is low in most nonpterodactyloids (here named bife- nestratans), intermediate in Rhamphorhynchus and Archaeopterodacty- loidea, and high in derived pterodactyloids. Incomplete fusion could also indicate loose connections between skull elements. However, another cru- cial anatomical requirement of a kinetic skull, the permissive kinematic linkage is absent in all pterosaurian taxa. The fact, that the presence of permissive kinematic linkages in the skull is also a prerequisite of all types of cranial kinesis, provides hard evidence that all members of Pter- osauria had akinetic skulls. Thus, the presence of the morphological attributes indicative of intracranial movements in some pterosaurs must be explained on grounds other than real potential for cranial kinesis. It could either be of mechanical or ontogenetic importance, or both. Alterna- tively, it might be considered as the morphological remnant of a real, ki- netic skull possessed by the diapsid ancestors of pterosaurs. Anat Rec, 294:813–830, 2011. VC 2011 Wiley-Liss, Inc. Key words: cranial kinesis; pterosaur; joint morphology; streptostyly INTRODUCTION Additional Supporting Information may be found in the Kinesis and Pterosaurs online version of this article. The occurrence of cranial kinesis among a variety of This article was published online on 31 March 2011. Subse- quently, it was determined that the Acknowledgements were tetrapods have long been recognized (see Frazzetta, 1962 incomplete, and the correction was published on 14 April 2011. for references), but the conceptual definition was first Grant sponsors: Hungarian Scientific Research Fund, Bolyai provided by Versluys (1910, 1912) who defined a kinetic Fellowship (A.O¨ .), Hantken Foundation; Grant number: OTKA skull as allowing any intracranial movements between PD73021 (Paleo Contribution No. 128); Grant sponsor: Hungarian the elements excluded that of the lower jaw. Cranial Natural History Museum, Eo¨tvo¨s Lora´nd University Budapest. kinesis as a phenomenon, being present in the earliest *Correspondence to: Edina Prondvai, Department of Paleon- tetrapods (movable palatoquadrates and palatal and fa- tology, Eo¨tvo¨s Lora´nd University, Pa´zma´ny Pe´ter se´ta´ny 1/c, cial elements; Iordansky, 1989) and in some extant tele- Budapest H-1117, Hungary. Tel.: 0036 20 526 00 60. osts and amphibians (Rieppel, 1978; Summers and E-mail: [email protected] Wake, 2005), is generally considered a plesiomorphic Received 23 July 2010; Accepted 1 December 2010 character (Iordansky, 1990) and is thought to be most DOI 10.1002/ar.21376 prominent within archosaurs and lepidosaurs (Herrel Published online 31 March 2011 in Wiley Online Library et al., 1999). However, clear evidence of true cranial (wileyonlinelibrary.com). VC 2011 WILEY-LISS, INC. 814 PRONDVAI AND O†SI Fig. 1. Three levels (A, B, C) of diapsid phylogeny gradually focus- among archosaurian clades focusing on the conspicuously different ing on the archosaurian clades (C). A, Interrelation of the major diapsid position of Pterosauria in the two cases (WST, Weighted Supertree; clades (after Lee, 2001); B, division of archosauriformes (after Sereno, SM, Supermatrix Tree). Groups of special significance for the EPB 1991); C, two possible outcomes for the phylogenetic relationships evaluation of this study are boldfaced. kinesis, which should be distinguished from slight move- (for further information see Supporting Information), ments occurring at many patent sutures and allowing was the only form of kinesis ever suggested for ptero- dissipation of mechanical stresses, exists unambiguously saurs. Most pterosaurologists have regarded the ptero- only in some squamates and birds among amniotes (Hol- saurian skull as universally akinetic (e.g., Wellnhofer, liday and Witmer, 2008). 1978; Buffetaut et al., 2002; Fastnacht, 2005). Nevertheless, some forms of cranial kinesis have been In the light of the dominance of more derived ptero- and probably will be suggested for numerous extinct ver- saurs with firmly fused skull bones in the fossil record, tebrates, particularly dinosaurs. In contrast to dino- this attitude is easy to understand. On the other hand, saurs, the notion of intracranial movements in another based on the apparent, although sometimes debated archosauromorph group, the pterosaurs is not so com- close affinities of pterosaurs to dinosaurs (Hone and mon. Except for the work of two authors, Arthaber Benton, 2008, and see Fig. 1 for the position of Pterosau- (1919) and Wild (1978, 1984), who regarded the Early ria in a broader phylogenetic context), for which cranial Jurassic Dorygnathus banthensis and the Upper Triassic kinesis has been proposed on several occasions (e.g., Col- Eudimorphodon ranzii, respectively, as having streptos- bert and Russell, 1969; Galton, 1974; Norman, 1984; tylic quadrate, and Bennett (1996a) who used the term Norman and Weishampel, 1985; Chiappe et al., 1998; ‘‘metakinetic skull’’ as a streptostylic character sugges- Mazzetta et al., 1998, see Supporting Information), and tive of archosauromorph nature of pterosaurs in his phy- on certain morphological attributes of some pterosaurian logenetic analysis, thus accepting Wild’s (1978, 1984) skulls it seems reasonable to pay more attention to the concept for Eudimorphodon, this issue has largely been potential of intracranial movements in pterosaurs. ignored. Hence, streptostyly, which refers to the antero- For the acquirement of the necessary theoretical back- posterior rotation of the quadrate about the otic joint ground, Supporting Information is provided which CRANIAL KINESIS IN PTEROSAURS 815 contains detailed information on basic concepts such as bony lamellae (e.g., craniofacial hinge in prokinesis the different forms, morphological correlates, functional of birds, see Supporting Information). If one of these significance, occurrence, origin, and evolution of cranial features is present, similarly to synovial joints, it can kinesis in other diapsid reptiles. In this Supporting In- assure mobility in the critical otic and basal regions of formation, the extremely kinetic skull of Serpentes is the skull. not regarded. The third criterion which has been cited by Holliday and Witmer (2008) as another morphological correlate of Osteological Aspects of Kinesis in Extant and cranial kinesis is the state of development of the protrac- tor muscles in the skull. They considered the presence of Extinct Taxa well-developed preotic and levator pendants as osteologi- To reveal features that are suggestive of cranial kine- cal indicators of protractor muscles (e.g., m. protractor sis several methods have been in use mainly in extant pterygoideus) which could have operated powered intra- taxa (Frazzetta, 1962, 1983; Smith and Hylander, 1985; cranial movements (Holliday and Witmer, 2008). The Patchell and Shine, 1986;